The Government Communications Security Bureau has written to all government departments advising them that there are "potential security issues" which they need to consider before deploying BlackBerry handheld computers.

Corporate affairs director Hugh Wolfensohn says GCSB's security advisory has been classified as confidential so he can't say what advice it contains.

It has been circulated to all departmental chief executives and their senior executives and IT managers.

The Australian Government's communications security watchdog, the Defence Signals Directorate, last month mandated that BlackBerrys should not be used to send or receive confidential, secret and top secret information or link to servers which hold such information.